X-ray reflectivity measurements of the binary liquid Ga-Bi alloy reveal a dramatically different surface structure above and below the monotectic temperature Tmono = 222°C. A Gibbs-adsorbed Bi monolayer resides at the surface in both regimes. However, a 30Å thick, Bi-rich wetting film intrudes between the Bi monolayer and the Ga-rich bulk for T>Tmono. The wetting film's internal structure, not hitherto measured, is determined with Å resolution, showing a concentration gradient not predicted by theory and a highly diffuse interface with the bulk phase.